Polymer nanocomposites for lithium battery applications

ABSTRACT

A single ion-conducting nanocomposite of a substantially amorphous polyethylene ether and a negatively charged synthetic smectite clay useful as an electrolyte. Excess SiO 2  improves conductivity and when combined with synthetic hectorite forms superior membranes for batteries. A method of making membranes is also disclosed.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/334,880filed Dec. 31, 2002.

CONTRACTUAL ORIGIN OF THE INVENTION

The United States Government has rights in this invention pursuant toContract No. W-31-109-ENG-38 between the U.S. Department of Energy (DOE)and The University of Chicago representing Argonne National Laboratory.

BACKGROUND OF THE INVENTION

Lithium ion secondary batteries are currently the best portable energystorage device for the consumer electronics market. Improved safety overconventional, fully liquid electrolytes provides a compelling rationalefor use of polymer electrolytes in rechargeable lithium batteries, butthese polymers often show insufficient conductivity or poor mechanicalproperties The dual ion-conducting nature of most polymer electrolytesalso poses problems. Investigations of the transport properties indicatethat cationic transference numbers are non-unity or even negative,indicating substantial transport by anionic complexes, particularly athigh salt concentration. Concentration gradients caused by the mobilityof both cations and anions in the electrolyte arise during celloperation, resulting in premature cell failure. This is a more severeproblem than in conventional liquid electrolytes because of the lowersalt diffusion coefficients and the relative immobility of the polymerhosts.

Attempts to design single ion conductors based on polymer-electrolyteswith fixed negative charges on the polymer have met with limitedsuccess; conductivities are relatively too low for practical use. Still,the ease of film fabrication, ability to withstand electrode volumechanges, and low temperature operation of a well-designed polymer-basedsystem provide distinct advantages over many ceramic single-ionconductors.

The conductivities of lithium-containing polymer-clay nanocomposites aregreatly enhanced over synthetic polymer single-ion conductors becauseonly cations are mobile in these materials. Preparation is simpler, theyare self-supporting, and generally have excellent mechanical properties.

The modification of polymer properties by the addition of anothermaterial, that is, a filler, has been studied for many years. Commonfillers such as glass fibers, carbon fibers and carbon black, pigmentsand minerals, including silicates, have been used to modify themacroscopic properties of the polymer, such as modulus and toughness. Inrecent years, a new class of materials have been developed by dispersinglayered silicates with polymers at the nanoscale level. These newmaterials have attracted wide interest because they often exhibitchemical and physical characteristics that are very different from thestarting material. In some cases, the silicates and polymers exist asalternating layers of inorganic and organic, as disclosed in Lemmon, J.P.; Wu, J.; Oriakhi, C.; Lerner, M. Electrochim. Acta., 1995, 40, 2245;Vaia, R. A.; Jandt, K. D.; Kramer, E. J.; Giannelis, E. P.;Macromolecules, 1995, 28, 8080; and Tunney, J. J.; Detellier, C. Chem.Mater., 1996, 8, 927. The possibility of improved mechanical,rheological, electrical, and optical properties and the ability toexercise control over existing physical and chemical behavior have ledto a large number of studies of these materials, including composites oflayer silicate clays with polyethylene oxide (PEO), epoxy resin,polystyrene, and a range of other thermoplastics and elastomers.

Polymer electrolytes exhibit high conductivity only in the absence of acrystalline phase, which impedes the transport of ions, and only attemperatures well above the glass-transition temperature (T_(g)). Anumber of methods have been used to prepare totally amorphous polymersof high conductivity, including random copolymers or branched blockcopolymers. However, the mechanical strength of these polymers is oftenpoor because of their low transition temperatures. Mechanical strengthcan be maintained by crosslinking of the polymer chains, but this comesat the expense of reduced conductivity. Another approach to increasingconductivity is to incorporate low molecular weight plasticizers intothe polymer.

Nanocomposite materials of PEO and phyllosilicates were first suggestedby Ruiz-Hitzky and Aranda, Ruiz-Hitzky, E.; Aranda, P. Adv. Mater.,1990, 2, 545, as candidates for polymer electrolytes. Within thesematerials, the polymer chains are intercalated between the silicatelayers. The polymer chains then provide a mobile matrix in which cationsare able to move. Nanocomposites of PEO and montmorillonite form alayered aluminosilicate clay. When this composite contains LiBF₄, itdisplays conductivities up to 2 orders of magnitude larger than that ofPEO itself at ambient temperatures. However, the addition of lithiumsalts, which is needed to obtain such conductivity values, is notdesirable for two reasons; the first one relates to a more complicatedsynthetic route and the second relates to the fact that transferencenumbers are not unity since in this case both cations and anions move.

SUMMARY OF THE INVENTION

An important object of the present invention is to provide an improvedelectrolyte for a lithium ion secondary battery.

Another object of the present invention to provide a singleion-conducting material of a substantially amorphous polyethylene etherand a negatively charged synthetic smectite clay.

Another object of the present invention is to provide a singleion-conducting polymer electrolyte in which a substantially amorphouspolyethylene ether is intercalated in a synthetic phyllosilicate clayhaving excess silicon dioxide distributed therein wherein thetransference numbers are greater than 0.9.

Yet another object of the present invention is to provide a lithium ionconducting polymer electrolyte in which polyethylene oxide isintercalated in phyllosilicate clay forming platelets having thicknessesin the 15-40 nanometer range.

Still another object of the present invention is to provide a bothindividual cells and battery of an alkali metal containing cathode andan anode separated by an electrolyte membrane of the type hereinbeforeset forth.

A final object of the present invention is to provide a method of makinga single ion-conducting material in which a single ion-conductingmaterial is formed by providing a single ion-conducting solidelectrolyte, providing and mixing negatively charged synthetic smectiteclay and a polyethylene ether to intercalate the polyethylene ether inthe clay, heating the mixture beyond the glass transition temperature ofthe clay and cooling.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention consists of certain novel features and a combination ofparts hereinafter fully described, illustrated in the accompanyingdrawings, and particularly pointed out in the appended claims, it beingunderstood that various changes in the details may be made withoutdeparting from the spirit, or sacrificing any of the advantages of thepresent invention.

FIG. 1 is a schematic illustration of intercalated polyethylene oxide ina synthetic lithium smectite;

FIG. 2 is a schematic representation of the sample holder used to obtainthe small angle x-ray scattering (SAXS) data;

FIG. 3 is an x-ray powder diffraction of the synthetic lithium smectitepowder with the inset showing major diffraction peaks;

FIG. 4 is an x-ray powder diffraction pattern of the polyethylene oxidepowder used to make the films of the present invention with the insetshowing major diffraction peaks;

FIG. 5 is an x-ray powder diffraction pattern of a film containingpolyethylene oxide and synthetic lithium smectite in a 1:1 mass ratiowith the inset showing major diffraction peaks;

FIG. 6 is a SAXS of a PEO/SLH in a 1.2:1 mass ratio film at roomtemperature with the inset showing diffraction peaks attributed to PEOand SLH;

FIG. 7 is a SAXS of the material illustrated in FIG. 6 after heating to60° C. under nitrogen at 5° C./min. showing the sharp peaks from PEObroadened indicating the PEO has lost its crystallinity;

FIG. 8(a) is a SAXS of the material in FIG. 7 heated to varioustemperatures and 8B is the same as FIG. 8(b) with the x-axis expanded;

FIG. 9 is a plot of the conductivity of the sample as a function oftemperature for a PEO/SLH 1:1 mass ratio;

FIG. 10(a) is a SAXS of a PEO/SLH 0.8:1 mass ratio film at varioustemperatures and FIG. 10(b) is the same as FIG. 10(a) with the x-axisexpanded;

FIG. 11(a) is a SAXS of a PEO/laponite film having a mass ratio of 1.2to 1 while FIG. 11(b) is the same as FIG. 11(a) with the x-axisexpanded;

FIG. 12 shows the TEM of a 1:1 PEO/SLH mass ratio nanocomposite membranewith small 20 nanometer silica spheres visible throughout thebackground; and

FIG. 13 is a schematic representation of a cell or battery incorporatingthe inventive electrolyte.

DESCRIPTION OF THE PREFERRED EMBODIMENT

We have prepared a series of nanocomposites containing PEO intercalatedin the layers of hectorite clays. These clays, also calledphyllosilicates, belong to the family of smectite clay minerals. Theyare composed of two tetrahedral silicate layers sandwiching a centraloctahedral layer in a so-called 2:1 arrangement, see FIG. 1. Inhectorite, isomorphous substitutions in the lattice of Li(I) for Mg (II)in the octahedral layers cause an overall negative charge that iscompensated by the presence of interlayer, or gallery, cations.Interlayer water is present and the cations are easily exchangeable. Alarge degree of preferential orientation in films prepared with naturaloccurring clays tends to occur, however, due to their large plateletsize (up to 1 μm). This can lead to non-conducting planes beingperpendicular to the current path and thus reduce the conductivity. Inthe present invention, the prior art problems were avoided by employingthe method developed by Carrado et al. in U.S. Pat. No. 5,308,808, theentire disclosure of which is incorporated herein by reference, whichinvolves direct hydrothermal synthesis and crystallization of hectoritewith smaller platelet size, termed synthetic lithium hectorite (SLH).Organic molecules can be either incorporated directly from the gel or bysubsequent intercalation. FIG. 1 shows a schematic structure ofintercalated PEO in a SLH. The circles in the gallery represent Li ions.

Even though there has been a considerable amount of experimental workrelated to the synthesis of nanocomposite films derived from PEO andmontmorillonite, a naturally occurring clay, using a melt intercalationprocedure, as electrolytes, their conductivity is low. The use ofpolyethylene ethers, such as PEO and synthetic smectite clays such asSLH and TEOS, a new synthetic hectorite made from the tetraethoxysilaneprecursor, see The Use of Organo and Alkoxysilanes in the Synthesis ofGrafted And Pristine Clays, K. A. Carrado, L. Xu, R. Csencsits, J. V.Muntean, Chemistry of Materials, 2001, 13, 3766-3773, the entiredisclosure of which is incorporated by reference, is new and hasprovided unexpectedly superior results as compared to the combination ofnatural clays and PEO. To the best of our knowledge, PEO/SLH or PEO/TEOSnanocomposites have not been used as polymer electrolytes andsurprisingly result in materials in which only the cation, preferably Liions, move through the electrolyte, and, therefore, the inventivematerials are properly described as single ion-conducting electrolytes.

Preparation of the SLH or TEOS clays via hydrothermal crystallization at100° C. of silica sol, magnesium hydroxide, and lithium fluoride can befound in detail in the incorporated '808 patent to Carrado et al. Inbrief, precursor clay gels are of the composition: 1.32 LiF, 5.3Mg(OH)₂, 8 SiO₂, n H₂O, to correlate with the ideal hectoritecomposition of Li_(0.66)[Li_(0.66)Mg_(5.34)Si₈O₂₀(OH,F)₄]. A typicalreaction begins by suspending the LiF with stirring in water.Separately, MgCl₂.6H₂O is dissolved in water and mixed with 2 N NH₄OH tocrystallize fresh Mg(OH)₂. Prior to use, this brucite source must bewashed several times with water to remove excess ions. It is then addedwet to the LiF solution. This slurry is stirred for 15-30 min beforeaddition of silica sol (ludox HS-30, Na⁺-stabilized, 30%). More or lesssilica sol may be added depending on the amount of excess SiO₂ desiredin the final product. The total volume is increased to afford a 2 wt %solids suspension, and is stirred and refluxed for 40-48 hours. Solidsare isolated by centrifugation, washed, and air-dried.

Colloidal suspensions of 1 g SLH/100 ml de-ionized water were stirredfor one-half hour. The desired amount of PEO (100,000 average molecularweight, from Aldrich) was then added, and the mixture stirred for 24hours. Mixtures contained 0.6, 0.8, 1.0, and 1.2 g of PEO/g of clay.Films were prepared by puddle-casting the slurries onto Teflon-coatedglass plates and air-drying. Further drying was carried out at 120° C.under an inert atmosphere for at least 48 hours. The typical thicknessof the films is about 40 μm. For comparative purposes, films ofPEO/laponite were prepared as disclosed in Doeff, M.; Reed, J. S. SolidState Ionics, 1998, 113-115, 109.

X-ray powder diffraction (XRD) patterns of SLH and PEO powders weredetermined using a Rigaku Miniflex, with Cu K_(α) radiation and a NaIdetector at a scan rate of 0.5° 2Θ/min and step size of 0.05.

In situ small angle x-ray scattering (SAXS) was carried out at theAdvanced Photon Source, (Basic Energy Sciences Synchrotron ResearchCenter CAT), Argonne National Laboratory. The SAXS intensity of theinvestigated material I(q) is the function of the angle of scattering(2θ) and the wavelength (λ) of the applied radiation. This relation canbe expressed as q=4π sin θ/λ. Monochromatic X-rays (18 keV) arescattered off the sample and collected on a 15×15 cm² CCD camera. Thescattered intensity is corrected for absorption and instrumentbackground. The differential scattering cross section is expressed as afunction of the scattering vector q. The value of q is proportional tothe inverse of the length scale (Å⁻¹). The instrument was operated witha sample-to-detector distance of 332 mm to obtain data at 0.1<q<3.0 Å⁻¹.

For these examples, a specially designed sample holder was used to heatup the sample and collect SAXS data at the same time. FIG. 2 shows adiagram of the sample holder. Films of about 1.25 cm in diameter and 40μm in thickness were placed in the sample holder and held using kaptontape. The furnace temperature program was set to ramp from roomtemperature to 150° C. at 5° C./min, and the gas flow of nitrogen wasstarted at room temperature. Temperature readings have an error of ±5°C. SAXS data were collected at room temperature, 60, 80, 100, 120, and150° C. in order to compare the structural results with the conductivityvalues. The sample holder with a piece of kapton tape heated at eachtemperature was used as the blank and all the SAXS data were correctedaccordingly.

AC impedance measurements as a function of temperature were obtained onfilms in sealed cells with lithium foil as the counter and workingelectrode, using a Solartron SI 1256 electrochemical interface and 1254frequency response analyzer. A Tenney Junior Environmental Test Chamberwas used to controlled the temperature of the cell with a precision of±0.5° C.

Transmission electron microscopy (TEM) was performed in a JEOL 100CXIITransmission Electron Microscope operating at 100 kV. Approximately 0.2mL of a 1:1 PEO/SLH slurry was placed into a vial and sonicated for 30seconds. Copper grids were then dipped into the resulting slurry. The Cugrids were allowed to dry for 2 hours in a vacuum oven at 100° C. Oncedry, the grids were inserted into non-tilt holders and loaded into theinstrument. Scale markers placed on the micrographs are accurate towithin three percent.

Understanding the structural changes of the PEO component in thenanocomposite films upon heating is crucial for predicting theconductivity of these materials. In situ SAXS is an excellent techniquefor deriving such information because of this particular instrument'stime-resolving capability and its high flux.

For comparison with SAXS data, X-ray powder diffraction of SLH and PEOpowders were obtained. FIG. 3 shows the X-ray powder diffraction of theSLH powder. The peaks are indexed as indicated on the graph of FIG. 3.The distance between clay sheets is given by the d₀₀₁ reflection andcorresponds to 12.7 Å, which includes one clay lattice unit at 9.6 Å.The gallery region therefore corresponds to 3.1 Å and contains Li(I)cations and water in this case. Because smectites are capable ofswelling, this region can easily accommodate one or more layers of PEO(2). FIG. 4 shows the diffraction pattern of the PEO powder used to makethe films. The peaks are quite sharp which indicates the crystallinenature of the starting material. An XRD pattern of a film containingPEO/SLH 1:1 ratio is shown in FIG. 5. The d₀₀₁ reflection has increasedby 5.89 Å, indicating that the PEO has been intercalated within the claygalleries.

FIG. 6 shows SAXS data obtained from a film made of PEO/SLH 1.2:1 massratio. The data was collected at room temperature. FIG. 6 shows clearlythe peaks that correspond to SLH and PEO. The d₀₀₁ peak is broader thanpresented in the XRD plots (because it is plotted here as Q in Å⁻¹), butthe spacing differs only by 0.42 Å. SAXS data was then collected at 60°C. and the results are shown in FIG. 7. It is clear that the structureof the polymer has changed as indicated by the near completedisappearance of the PEO crystalline peaks. It is therefore believedthat the polymer chains have relaxed inside the clay layers. Otherevidence of such relaxation is the decrease in d₀₀₁ spacing, whichindicates a more dense polymer phase. Under these circumstances, thepolymer matrix is more mobile and the lithium ions associated with thepolymer can have higher transference number, leading to a higherconductivity. The samples were also heated at 80, 100, 120, and 150° C.and the results are shown in FIGS. 8 a) and b), wherein FIG. 8 b is FIG.8 a with the x-axis expanded, the same as FIGS. 10(a)(b) and FIGS.11(a)(b). Except for complete disappearance of the PEO peaks at 80° C.,there are no other polymer structural changes. Due to the PEO content ofthese nanocomposites, it is possible that part of the polymer remainsadsorbed at clay surface and that after heating the samples, this PEOcan re-intercalate. After the samples were heated at 150° C., they werecooled down at room temperature and a SAXS measurement was performed.The results suggested that the lost of PEO crystallinity isirreversible, that is, no crystalline peaks were observed.

The conductivity of the nanocomposite was determined at the sametemperature as the SAXS in situ data to correlate the changes in thenanocomposite structure with conductivity. FIG. 9 shows a plot ofconductivity as a function of temperature of the nanocomposite withnominal composition PEO/SLH 1:1 mass ratio. As known, the conductivityof the polymer nanocomposites increases as the sample is heated fromroom temperature (26.0° C.) to 150° C. As shown in the plot, the largestincrease in conductivity occurs between room temperature and 60° C., inaccordance with the decrease on the polymer crystallinity. Similarbehavior was observed for the PEO/SLH 0.6:1, 0.8:1, and 1.2:1 samples.

Transference numbers were obtained following the procedures outlined byDees et al. in Chen, H. W.; Chiu, C. Y.; Chang, F. C. J. Polym. Sci.,Part B, Polm. Phys. 2002, 40, 1342. As anticipated for a single ionconductor, the transference numbers obtained as a function oftemperature were very close to unity (Table 1). Same as with theconductivity values, the largest increase in the numbers is observedfrom room temperature to 60° C., in accordance to the conductivityvalues and the loss of polymer's crystallinity.

In situ studies were also performed on the nanocomposites samples withratios of 0.6, 0.8, and 1.0 g of PEO/g of clay. The results of the 0.8 gPEO/SLH are shown in FIGS. 1110 a and 10 b. The changes are identical tothe other films (results of the 1:1 and 0.6 not shown). The onlydifference resides on the intensity of the PEO peak at 4.47 Å, whichdecreases slightly as the amount of PEO in the film decreases.

For comparative purposes, in situ SAXS studies were also performed onfilms made with PEO/laponite at different mass ratios. FIGS. 11(a) and11(b) shows the data taken at different temperatures of a film made witha mass ratio of PEO/laponite of 1.2:1. The data is similar to thePEO/SLH; however, the conductivity of the PEO/SLH films is at least oneorder of magnitude higher (at 60° C.) than the films made ofPEO/laponite. The SLH has larger particle size than laponite and about20% silica impurity and either of which may be responsible for thehigher conductivity. FIG. 12 shows the TEM of a 1:1 PEO/SLH membrane,wherein small 20 nm disks due to silica spheres are visible throughoutthe background. Commercially available laponite does not contain silicaparticles. Other clay materials contain negligible amounts of silicaimpurities. For example, when Li-fluorohectorite is made by hightemperature solid-state melting process, it does not contain any silica.SAz-1 montmorillonite has at most only about 1% quartz and similarlysmall amounts of cristobalite or opal as the only silica impurities.Swy-2 is about 95% clay when purified and 4% of the impurities arequartz. Most montmorillonites are fairly pure and do not have muchsilica. The synthetic route disclosed herein leads to the production ofpolymeric nanocomposites with enhanced conductivity without addition ofceramic or oxide fillers.

In situ SAXS studies show that the structural changes, as a function oftemperature, of polymer nanocomposites derived from PEO/SLH, can beobtained with detail. At 60° C., PEO losses its crystallinity and it isat this point where the films become more conductive, as also indicatedby the high conductivity (4.87×10⁻³ S/cm) and the almost unitytransference number (0.95). It has been indicated that highcrystallinity in polymers is unfavorable for ionic conductivity. Whenthe polymer phase becomes amorphous, there is an increase of thedisordered regions responsible for the ion conduction. There are noother structural changes upon heating the films to 150° C., indicatingthe stability of the nanocomposites.

Referring now to Table 1, the transference numbers for a variety ofdifferent PEO/SLH mass ratio membranes as a functional temperature isreported. As seen from the left hand column of Table 1, the mass ratioof the polyethylene oxide (ether) to the synthetic hectorite was variedfrom 06:1 to 1.2:1. The transference numbers for each of the variousmembranes were reported from room temperature (RT), all the way to 150°C. As may be seen from the Table, the transference numbers as high as0.95 were obtained for certain membranes at temperatures ranging from60°-100° C. while transference numbers in general above 0.90 werereported for a variety of membranes. This Table shows the superiornature of the single ion-conducting electrolytes of the presentinvention. Transference numbers approaching unity have been obtainedunder a variety of conditions and these numbers are a distinctimprovement over dual ion-conducting polymer electrolytes known at thepresent time.

It is seen that there has been disclosed a single ion-conductingmaterial of a composite of a substantially amorphous polyethylene etherand a negatively charged synthetic smectite clay. More particularly, wehave disclosed herein single ion-conducting membranes having thicknessesless than about 60 micrometers comprised of synthetic clay plateletsless than 40 nanometers in thickness. In general, the material of thepresent invention has superior conductivity properties, in part, due tothe excess silicon dioxide present in the synthetic smectite clay madein accordance with the method of the present invention. Moreparticularly, the excess SiO₂ is present in an amount not less thanabout 15% by weight and generally in an amount from between about 15%and 25% by weight in excess of the stoichiometric amount of silicondioxide required.

The single ion-conducting material of the present invention hascharacteristics which may be varied according to the molecular weight ofthe polyethylene ether or in the specific case illustrated, polyethyleneoxide. Molecular weights in the range of from about 80,000 to about250,000 have been found to be useful with molecular weights generally inthe range of about 80,000 to about 100,000 range being preferred. Incertain instances, mixtures of various molecular weight polyethyleneoxides have been used such as 80% by weight having a molecular weight ofabout 80,000 and 20% by weight having a molecular weight of about10,000, an improvement because the combination lowers the Tg of thematerial. The invention is intended to cover polyethylene oxides orethers having a variety of different molecular weights.

Mass ratios of the polyethylene ether to the clay has been found to beeffective in the range of from about 0.5:1 to about 3:1. Preferably, theratio is about 1.5:1 and most preferably 1.2:1. In general, the singleion-conducting material is cation conducting and more particularly, theinvention involves an alkali metal ion and most specifically lithiummetal ion. Generally, the negatively charged smectite clay is aphyllosilicate and more particularly is a hectorite. Within thepreferred embodiment the hectorite is a lithium hectorite. As statedbefore, the polyethylene oxide is intercalated between layers of thesynthetic clay. Membranes made with the inventive material havethicknesses less than about 6.0 micrometers and most preferably in therange of from about 40 to about 60 micrometers. The hectorite plateletsthemselves have a thickness of less than about 40 nanometers and mostpreferably in the range of from about 15 to about 40 nanometers. Asbefore stated, it is preferred that the ion transport number is greaterthan 0.9 and most preferably about 0.95.

A variety of substrates may be used to carry the membranes of thepresent invention. In general, the preferred substrates are eithersilicon or glass. Membranes of the present invention have been subjectedup to about 20,000 psi without rupture. As is known in the art, there isa trade off or compromise between conductivity and mechanical strength.The thicker the membrane the stronger but less conductive. In generalthicknesses in the range of 40-60 micrometers is preferred. Oneadvantage of using mixtures of various molecular weight ethers is thatthe T_(g) can be lowered by as much as 2-3° C. if up to about 20%polyethylene oxide of about 10,000 molecular weight is mixed with about80% molecular weight polyethylene oxide of between about 80-100,000.

As seen from the foregoing, excess silicon dioxide in the amount ofabout 20% is preferred, see FIG. 2. The amount of SiO₂ is controlled bythe method as disclosed in the previously cited Carrado '808 patent. Ingeneral, excess silicon dioxide in the range of from about 15 to about25% is preferred. TABLE 1 Transference numbers obtained for differentPEO/SLH mass ratio as a function of temperature. Temperature, ° C.Composition RT 60 80 100 120 150 PEO/SLH t_(Li+) 0.6:1 0.88 0.92 0.920.93 0.93 0.93 0.8:1 0.90 0.95 0.95 0.95 0.94 0.94   1:1 0.87 0.91 0.920.93 0.93 0.93 1.2:1 0.87 0.90 0.90 0.91 0.91 0.92

Referring to FIG. 13, there is illustrated a battery for lithiumion-secondary cells and batteries consisting of several cells. As shownschematically in FIG. 13, the cell 10 has a negative electrode 12separated from a positive electrode 16 by an electrolyte 14, allcontained in an insulating housing 18 with suitable terminals (notshown) being provided in electronic contact with the negative electrode12 and the positive electrode 16. Binders and other materials normallyassociated with the electrolyte, the negative or positive electrodes arewell known in the art and are not described herein, but are included asis understood by those of ordinary skill in this art. Cells 10 formbatteries, as is well known, by connecting cells 10 in parallel and/orin series.

While particular embodiments of the present invention have been shownand described, it will be appreciated by those skilled in the art thatchanges and modifications may be made without departing from theinvention in its broader aspects. Therefore, the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of the invention. The matter set forth in theforegoing description and accompanying drawings is offered by way ofillustration only and not as a limitation. The actual scope of theinvention is intended to be defined in the following claims when viewedin their proper perspective based on the prior art.

1-19. (canceled)
 20. A single ion-conducting polymer electrolyte,comprising a nanocomposite of a substantially amorphous polyethyleneether intercalated in a negatively charged synthetic phyllosilicate clayhaving excess SiO₂ therein.
 21. The single ion-conducting polymerelectrolyte of claim 20, wherein said synthetic phyllosilicate clay hasplatelets having a thickness in the range of from about 15 to about 40nanometers.
 22. The single ion-conducting polymer electrolyte of claim21, wherein said excess SiO₂ is present in the range of from about 15%to abut 25%.
 23. The single ion-conducting polymer electrolyte of claim22, wherein said excess SiO₂ is present in an amount of about 20%. 24.The single ion-conducting polymer electrolyte of claim 22, wherein saidphyllosilicate clay is a hectorite.
 25. The single ion-conductingpolymer electrolyte of claim 24, wherein said excess SiO₂ is present isin the form of spheres about 20 nanometers in diameter.
 26. The singleion-conducting polymer electrolyte of claim 25, wherein the mass ratioof polyethylene ether to hectorite clay is in the range of from about0.5:1 to about 3:1.
 27. The single ion-conducting polymer electrolyte ofclaim 26, wherein said electrolyte is in the form of a membrane having athickness in the range of from about 40 to about 60 micrometers.
 28. Thesingle ion-conducting polymer electrolyte membrane of claim 27, whereinsaid membrane is on a backing material of glass or silicon.
 29. Thesingle ion-conducting polymer electrolyte membrane of claim 28, whereinsaid negatively charged hectorite clay has Li+ ions therein.
 30. Thesingle ion-conducting polymer electrolyte membrane of claim 29, whereinat least a portion of said polyethylene ether is polyethylene oxidehaving a molecular weight between about 80,000 and about 250,000. 31.The single ion-conducting polymer electrolyte membrane of claim 30,wherein the mass ratio of polyethylene oxide to clay is in the range offrom about 0.5:1 to about 1.5:1.
 32. The single ion-conducting polymerelectrolyte membrane of claim 31, wherein the ion transport number isgreater than 9.0.
 33. A single lithium-ion conducting polymerelectrolyte membrane, comprising a nanocomposite of substantiallyamorphous polyethylene oxide intercalated in a negatively chargedsynthetic phyllosilicate clay having not less than about 15% excessSiO₂.
 34. The single lithium-ion conducting polymer electrolyte membraneof claim 33, wherein said phyllosilicate clay has platelets having athickness in the range of from about 15 to about 40 nanometers and theexcess SiO₂ is in the form of spheres about 20 nanometers in diameter.35. The single lithium-ion conducting polymer electrolyte membrane ofclaim 34, wherein the lithium ion transport number is greater than 90.36. The single lithium-ion conducting polymer electrolyte membrane ofclaim 35 and further including a substrate carrying said membrane. 37.The single lithium-ion conducting polymer electrolyte membrane of claim36, wherein said substrate is silicon or a glass.
 38. The singlelithium-ion conducting polymer electrolyte membrane of claim 37, whereinthe membrane has a thickness in the range from about 40 to about 60micrometers; and the mass ratio of polyethylene oxide to clay is in therange of from abut 0.5:1 to about 1.5:1. 39-50. (canceled)